The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, HDDs have been desired to store more information in its limited area and volume. A technical approach to this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, it is useful to increase the quality of the magnetization transition which determines the signal-to-noise ratio (SNR) of the bit information stored to the magnetic medium. In order to achieve this with conventional techniques, a write bubble that is faster than the transition speed of the recording medium is generated. Therefore, many attempts have been made to shorten a magnetic circuit length for a magnetic head in order to further improve the high frequency properties.
A specific structure of a magnetic circuit of a magnetic head is shown in Japanese Unexamined Patent Application Publication No. 2011-14207, specifically in FIG. 4, for example. In this example, a non-magnetic body is disposed between a trailing shield and a main pole at a media-facing surface. The trailing shield is connected to an upper return pole (URP). The URP is positioned above an insulator that insulates the coil which wraps around and is connected to an auxiliary pole at a rear portion thereof. The auxiliary pole is laminated in close contact with the main pole. In perpendicular magnetic recording, the magnetic flux produced at the media-facing surface returns to the URP via the soft magnetic backing layer of the medium, and forms a magnetic loop by returning to the main pole via the auxiliary pole.